The aim of these studies is to use the electron microscope in conjunction with other techniques to elucidate the structural details of large enzymes and other biological molecules. The studies will concentrate mainly on examinations of several biotin-containing enzymes including: transcarboxylase from the propionic acid bacteria and pyruvate carboxylase from several species of animal liver, yeast and bacterial species. Specific problems include the interaction of these enzymes with antibodies prepared against biotin or against the specific enzymes, interaction with avidin, and the shape, numbers and conformation of individual subunits of the proteins. In addition, the studies will be extended to several other enzymes including acetyl-CoA deacylase, phosphoenolpyruvate carboxykinase, and phosphoenolpyruvate carboxylase.